Add VerificationLevel::Higher
Add VerificationLevel::Higher

A new verification level was added for guilds with a value of 4, which
means "Must have a verified phone on their Discord account."

Flat/serenity,Roughsketch/serenity,acdenisSK/serenity,Lakelezz/serenity,zeyla/serenity,zeyla/serenity.rs,eLunate/serenity